The present invention relates generally to the field of orthopaedics, and more particularly, to an implant for use in arthroplasty.
The invention relates to implantable articles and methods for manufacturing such articles. More particularly, the invention relates to bone prosthesis and processes for manufacturing the same.
There are known to exist many designs for and methods for manufacturing implantable articles, such as bone prosthesis. Such bone prosthesis include components of artificial joints, such as elbows, hips, knees, and shoulders. An important consideration in the design and manufacture of virtually any implantable bone prosthesis is that the prosthesis has adequate fixation when implanted within the body.
Early designs of implantable articles relied upon the use of cements such as polymethylmethacrylate to anchor the implant. The use of such cements can have some advantages, such as providing a fixation that does not develop freeplay or does not lead to erosion of the joining bone faces postoperatively. However, the current trend is to use these cements to a lesser extent because of their tendency to lose adhesive properties over time and the possibility that the cement contributes to wear debris within a joint.
Recently, implantable bone prosthesis have been designed such that they encourage the growth of hard tissue (i.e., bone) around the implant. The bone attachment usually occurs and growth is promoted when the surface of the implantable bone prosthesis is irregular or textured. The interaction of newly formed hard tissue in and around the textured surface of the implantable bone prosthesis has been found to provide a good fixation of the prosthesis within the body. A greater degree of bone fixation can usually be achieved where bone-engaging surfaces of an implantable bone prosthesis are more porous or irregular.
Porous or irregular surfaces can be provided in implantable articles by a variety of techniques. In some instance, an irregular surface pattern or surface porosity is formed in an implantable bone prosthesis by embossing, chemical etching, milling or machining.
Another problem which has been observed in the use of known hip joint systems relates to the proper distribution of stresses within the prosthesis and throughout the surrounding bone. If too little stress is applied to the bone, resorption can occur leading to atrophy of the affected area. Too much stress may also lead to resorption and atrophy, or may result in an undesirable hypertrophy of the affected area. In some prior art, femoral stem designs excessive forces are transmitted through the relatively rigid stem to the distal portion, resulting in hypertrophy of the bone surrounding the distal portion, and atrophy of the bone surrounding the proximal portion of the stem. Accordingly, there exists a need for an improved hip joint prosthesis which addresses these needs and other problems of prior hip joint designs.
Attempts have been made to provide for proximal loading of the prosthesis within the bone. For example, in U.S. Pat. No. 5,004,075 to Vermeire a series of parallel spaced apart linear grooves 28 were positioned perpendicular to the longitudinal axis 22 of the neck of the prosthesis. A second set of parallel spaced apart linear grooves 29 were positioned generally perpendicular to the grooves 28. These grooves serve to provide support in the proximal region of the stem of this prosthesis.
In U.S. Pat. No. 4,865,608 to Brooker, Jr. a series of spaced apart parallel grooves 24 and 24xe2x80x2 were positioned along the outer periphery of the opposite sides of the proximal portion of the stem. The grooves were positioned at an angle of approximately 70 degrees with respect to the longitudinal axis of the stem.
In total hip arthroplasty, initial and long term success are achieved through the use of a device which is designed to provide at least two features. The first of these features is the stable initial or immediate postoperative fixation within the femur. The second feature is the means to provide an optimal environment for a long-term stability in the femur. In the past, fixation has been achieved through the use of bone cement, porous coatings and bio-ceramics. Bio-ceramics includes such compositions as hydroxyapatite and tricalcium phosphates. Many of these cements, coatings and bio-ceramics have provided good clinical outcomes, however, none have addressed the biomechanics of load transmission through the proximal femur.
Methods of achieving femoral fixation in the prior art have met with some success. These methods include simple press fit, surface roughness, porous coating, and bioceramics. Many devices have included texturing to transfer load in favorable mechanical modes. However, none of the prior art devices have designed the texturing (steps) to transfer load along the natural load paths of the proximal femur. The Brooker patent has angled steps on the anterior and posterior face, however, on the medial edge, the steps are longitudinal. This design will not appropriately transmit load to the medial calcar. The Vermeire patent has no steps on the medial edge, posing a similar problem.
A commercially available product from Stryker Howmedica Osteonics known as the Omni Fit Femoral Stem has normalization features which transmit load directly vertical. This load path is not natural. This device has no medial steps. A commercially available product from DePuy Orthopaedics, Inc., the JMP S-ROM transmits axial loads, but again, does not follow the natural load path.
Accordingly, a need has arisen for a prosthesis which achieves fixation to the long bone by designing features to transfer load along the natural load paths of the proximal long bone.
The present invention includes a proximal long bone prosthesis which has been designed to provide initial stability and long term fixation through a series of features capable of transmitting load to the proximal long bone in a manner consistent with the natural load paths of the long bone. The long bone may be a femur, a humerus or any other long bone.
The present invention allows reconstruction of the proximal long bone with a device that is specifically designed to provide stable initial fixation and long term stability by optimally transferring load along the natural load lines through the femur. The load paths through the proximal long bone are seen by both the alignment of the trabeculae in the proximal cancellous bone and by the direction of the layers or lamellae in the cortical bone.
This device achieves initial fixation through a press fit. The press fit is achieved with a properly designed preparation instrumentation. Long term stability is achieved through a series of steps which are aligned normal to the trabeculae of the proximal femur cancellous bone and the lamellae of the proximal femoral cortex. The steps transmit load normal to their surface and hence along the natural femoral load lines. This replication of the natural femoral load paths lead to favorable remodeling of the proximal long bone. This fixation mode may be further enhanced with a bone in growth/on growth surface such as for example surface roughness, porous coating and/or bioceramics.
According to one embodiment of the present invention, a ball and socket joint prosthesis for use in arthroplasty is provided. The prosthesis includes a body for implantation at least partially within the medullary canal of a long bone. The long bone defines trabeculae in the proximal cancellous bone and lamellae in the cortical bone. The body includes a proximal portion and a distal portion. The proximal portion has a medial periphery and includes surface features on a substantial portion of the periphery of the proximal portion. The surface features are positioned to optimally transfer load from the prosthesis to the long bone.
According to another embodiment of the present invention, a hip-joint prosthesis for use in arthroplasty is provided. The prosthesis includes a body for implantation at least partially within the medullary canal of a long bone. The long bone has trabeculae in the proximal cancellous bone and has lamellae in the cortical bone. The body includes a proximal portion and a distal portion. The proximal portion has a medial periphery and includes a plurality of ribs extending from a substantial portion of the periphery of the proximal portion. The ribs are positioned so that the first direction of the ribs is from about 70 degrees to about 110 degrees with respect to the trabeculae in the proximal cancellous bone, the normal lamellae in the cortical bone or the medial periphery of the proximal portion of said body.
According to yet another embodiment of the present invention, a joint prosthesis for use in arthroplasty is provided. The prosthesis includes a body for implantation at least partially within the medullary canal of a long bone. The long bone includes trabeculae in the proximal cancellous bone and lamellae in the cortical bone. The body includes a proximal portion and a distal portion. The proximal portion has a medial periphery and includes surface features on a substantial portion of the periphery of the proximal portion. The surface features are positioned to optimally transfer load from the prosthesis to the long bone.
According to a further embodiment of the present invention, a stem for use in a joint prosthesis for implantation at least partially within the medullary canal of a long bone is provided. The long bone includes trabeculae in the proximal cancellous bone and lamellae in the cortical bone. The stem includes a proximal portion and a distal portion. The proximal portion has a medial periphery and surface features on a substantial portion of the periphery of the proximal portion. The surface features are positioned to optimally transfer load from the prosthesis to the long bone.
According to another embodiment a method for producing a joint prosthesis for use in arthroplasty is provided. The method includes the steps of providing a body including a proximal portion and a distal portion, the proximal portion having a medial periphery thereof, placing surface features on a substantial portion of the periphery of the proximal portion of the body, positioning the surface features to optimally transfer load from the prosthesis to the long bone, and implanting the prosthesis at least partially within the medullary canal of a long bone.
The technical advantages of the present invention include the ability to transmit loads to the proximal femur along the natural load lines. The load lines or load paths through the proximal femur are seen by both the alignment of the trabeculae in the proximal cancellous bone and by the direction of the lamellae in the cortical bone. This invention achieves initial fixation through a press-fit achieved with properly design preparation instrumentation. Long term stability is achieved through a series of steps which are aligned normal to the trabeculae of the proximal femoral cancellous bone and the lamellae of the proximal femoral cortex. The steps transmit load normal to their surface and hence along natural femoral load lines.
Another technical advantage of the present invention includes the ability to provide long term stability and fixation by providing an environmental optimum for femoral bone remodeling. The long term stability achieved through the series of steps which are aligned normal to the trabeculae of the proximal femoral cancellous bone and the lamellae of the proximal femoral cortex transmit load normal to their surface and hence along the natural femoral load lines. This replication of the natural femoral load paths leads to favorable remodeling of the proximal femoral bone. This fixation mode may be further enhanced with a bone ingrowth or ongrowth surface, for example, by providing for surface roughness, porous coating and bioceramics.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions and claims.